The present invention relates to a method for photochemically making visible residual moisture distributions in photographic wet film layers subjected to an oncoming flow, by applying a swelled photographic film to the surface subjected to the flow, by conducting a gas over it and by subsequent development of a residual moisture photogram by means of photographic developers.
According to known methods, residual moisture distributions in photographic wet film layers subjected to a flow can be made visible by photochemical means. The wet film diffusion method is based on the conversion of residual moisture profiles in films exposed to a flow into half-tone blackening profiles analogous to moisture. The development can be accomplished by sulfide seeding or by post-exposure. With post-exposure, the photographic developer subsequently incorporated in the film generates silver half-tone images analogous to moisture at points of the residual moisture profile. Dry points on the film remain bright (see U.S. Pat. No. 3,774,225). The post-exposure method and the sulfide seeding method are disturbed by the effect of daylight and must, therefore, be carried out under dark room conditions. In order to be able to work in daylight, it is necessary to convert the residual moisture profile of the exposed wet film into a brown silver sulfide image in a mixture of hydrogen sulfide and air according to the so-called hydrogen sulfide method ("Sulfide Seeding Method"). This requires not only fairly large amounts of hydrogen sulfide gas, but also very accurately defined gas mixtures, which are difficult to prepare, for the quantative densitometric evaluation of the silver sulfide half-tone photograms.
For improving these methods it has been proposed in commonly-assigned U.S. Ser. No. 936,948 now U.S. Pat. No. 4,250,249 to first immerse the film exposed to the gas stream in an alcoholic (ethanolic) sodium hydroxide solution (Bath 1--alkalizing the residual moisture remaining in the film). After removing residual liquid on the film surface by means of a calender, the film is subsequently immersed in a neutral aqueous solution with a reducing agent suitable as a photographic developer, for example, hydroquinone (Bath 2). Silver development takes place only at the alkali-containing points of the film. This method, which works successfully in daylight, requires that the operating temperatures of the baths be kept constant.